New paper on active black holes affecting star formation rates!

Good news everyone, another Galaxy Zoo paper was published today! This work was led by yours truly (Hi!) and looks at the impact that the central active black holes (active galactic nuclei; AGN) can have on the shape and star formation of their galaxy. It’s available here on astro-ph: and will soon be published in MNRAS.

Turns out, despite the fact that these supermassive black holes are TINY in comparison to their galaxy (300 light years across as opposed to 100,000 light years!) we see that within a population of these AGN galaxies the star formation rates have been recently and rapidly decreased. In a control sample of galaxies that don’t currently have an AGN in their centre, we don’t see the same thing happening. This phenomenon has been seen before in individual galaxies and predicted by simulations but this is the first time its been statistically shown to be happening within a large population. It’s tempting to say then that it’s the AGN that is directly causing this drop in the star formation rate (maybe because the energy thrown out by the active black hole blasts out or heats the gas needed to fuel star formation) but with the data we have we can’t say for definite if the AGN are the cause. It could be that this drop in star formation is being caused by another means entirely, which also coincidentally turns on an AGN in a galaxy.


A random sample of galaxies which host a central active black hole used in this work. The disc vote fraction classification from Galaxy Zoo 2 is shown for each image. Images from SDSS.

These galaxies were also all classified by our wonderful volunteers in Galaxy Zoo 2 which meant that we could also look whether this drop in the star formation rate was dependent on the morphology of the galaxy; turns out not so much! If the drop in the star formation rate is being caused directly by the AGN (and remember we still can’t say for sure!) then the central black hole of a galaxy doesn’t care what shape galaxy it’s in. An AGN will affect all galaxies, regardless of morphology, just the same.



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5 responses to “New paper on active black holes affecting star formation rates!”

  1. JohnF says :

    Just read it – Good paper Becky, well done.

  2. Peter Dzwig says :

    I agree. Fascinating stuff. Would a corollary of this work be that IF a (sufficiently large) BH occurred locally during formation of a galaxy, not even necessarily at the centre, then the rate of star-formation in the BH’s vicinity would be expected to drop?

    • chrislintott (@chrislintott) says :

      I suspect so, but ‘sufficiently large’ is important. There’s a big gap between stellar mass black holes and the supermassive ones which amount to at least hundreds of thousands of solar masses. My guess is you have to be in the latter category to do much more than affect your very local environment.

  3. Emily says :

    I love black holes they are so interesting I may only be 14 but this is my favorite topic to talk about! I really want to be a astronomer and I have a lot of questions that I desperately want answered I actually have a theory about black holes. But google is no help and well no 8th grader even has the attention span at my school to know what a black hole even is.

    • Brooke Simmons says :

      Hi Emily, that’s great that you love black holes, and you’ll have a lot of company here! If you want to, you can post your questions here as a reply, and we will try to answer them when we can. Or, you can post on our Talk pages ( and get answers from other members of the GZ community.

      It’s also really great to form hypotheses about the things you’re most interested. The most important feature of a good hypothesis is that it should be testable, so whatever your hypothesis is, think about how you’d test it. Some hypotheses are only testable in theory (for example, we can’t *yet* go drop things into a black hole to see what happens), but others are testable based on observations we can make now.

      Anyway, good luck with your studies and keep on learning about black holes! 🙂


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